Solid mixtures of alpha-hydroxycarbonyl derivatives of alpha-methylstyrene oligomers and their use

ABSTRACT

The present invention refers to solid mixtures of alpha hydroxycarbonyl derivatives of alpha-methylstyrene oligomers containing at least 90% of the dimer isomers, the dimer isomer ratio being between 2.5 and 7, to their preparation and to their use as photoinitiators in photopolymerisation.

The present invention refers to solid mixtures of alpha-hydroxycarbonylderivatives of alpha-methylstyrene oligomers and to their use asphotoinitiators in light-induced radical photopolymerisation of acrylicsystems.

In particular the invention refers to the preparation of the solidmixtures, which can be easily handled and which mainly contain one ofthe dimer isomers.

According to a fundamental aspect of the invention it was surprisinglyfound that the solid mixtures exhibit a higher reactivity than the oneexpected from the to purity of the dimer isomers.

The use of oligomeric photoinitiators in the photopolymerisation hasseveral advantages in comparison to the use of monomericphotoinitiators, such as a lower migratability of the photoinitiatorfrom the formulation and a reduced amount of volatile compounds derivedfrom their photodecomposition.

Those characteristics are important for the industrial use because theyreduce the risk of contamination of the finished product with unwantedcompounds.

Among oligomeric photoinitiators the alpha-hydroxycarbonyl derivativesof dimers and trimers of alpha-methylstyrene are known.

These photoinitiators are described, for instance, in U.S. Pat. No.4,987,159.

They are mainly constituted by a mixture of dimer and trimer isomers.

At room temperature the mixture is a very highly viscous product thatcannot be easily used as such in industrial applications.

In the present text with the expression “alpha-hydroxycarbonylderivatives of oligomers of alpha-methylstyrene” we refer to compoundsof Formula I, wherein n is a number equal or greater than 0.

The alpha-hydroxycarbonyl derivatives of oligomers ofalpha-methylstyrene are a product with a pour point of from 40 to 50° C.In the present text, this product is indicated as “high viscositymixture”.

Another aspect of the invention is a process for the precipitation of asolid mixture from said high viscosity mixture.

According to another aspect of the invention the solid mixture obtainedby precipitation from the high viscosity mixture mainly consists of thedimer isomers in a modified ratio.

In particular the concentration of dimer isomers 5 and 6 increases from60–85% (w/w) in the high viscosity mixture to about 90–98% (w/w) in thesolid mixture and the ratio of the dimer isomers 5 and 6 from 1.5–2.3 to2.5–7.0.

The expression “dimer isomer 5” refers to the product of Formula II.

The expression “dimer isomer 6” refers to the product of Formula III.

In patent U.S. Pat. No. 4,987,159, the Applicant describes aprecipitation of the mixture of alpha-hydroxycarbonyl derivatives ofdimers and trimers of alpha-methylstyrene, without reporting amodification of the ratio between the dimer isomers 5 and 6 in theobtained mixture.

According to a fundamental aspect of the present invention, the solidmixtures of alpha-hydroxycarbonyl derivatives of oligomers ofalpha-methylstyrene containing at least 90% of the dimer isomers 5 and 6are disclosed, the ratio of the dimer isomer 5 and the dimer isomer 6being between 2.5 and 7.

Another aspect of the present invention is a process for the preparationof the to solid mixtures exhibiting a higher reactivity than the one dueto the increase in purity.

This behavior suggests that the reactivity of the dimer isomers isregiospecific.

The solid mixtures of alpha-hydroxycarbonyl derivatives of oligomers ofalpha-methylstyrene of the present invention are obtained byprecipitation from a high viscosity mixture containing at least 60% ofthe dimer isomers of the above mentioned derivatives.

Such a high viscosity mixture can be prepared as reported for instancein U.S. Pat. No. 4,987,159.

The process for the preparation of the solid mixtures ofalpha-hydroxycarbonyl derivatives of oligomers of alpha-methylstyrene ofthe present invention consists in dissolving the high viscosity mixtureof alpha-hydroxycarbonyl derivatives of oligomers of alpha-methylstyrenein a solvent with a polarity between 0.1 and 0.7, preferably between0.25 and 0.6, with a ratio solvent/high viscosity mixture between 0.2and 4, preferably between 0.4 and 2.5, keeping the solution at atemperature below 40° C. for from 10 to 60 hours and collecting the thusobtained solid mixture.

The polarity of the solvent (ε°) corresponds to the absorption energymeasured on Al₂O₃.

According to a further aspect of the invention the use in radicalphotopolymerisation of formulations containing at least one unsaturatedcompound of the solid mixtures of alpha-hydroxycarbonyl derivatives ofoligomers of alpha-methylstirene, containing at least 90% of the dimerisomers 5 and 6, the ratio of the dimer isomers 5 and 6 being between2.5 and 7 is disclosed.

The solid mixtures of the present invention are particularly suitable inphotopolymerisation of formulations containing unsaturated compounds ofthe class of acrylic or methacrylic derivatives, or mixtures thereof,and are preferably used as photoinitiators in low yellowing paints andlacquers, in adhesives, in photocrosslinkable compositions for printingplates and in the field of graphic arts.

The isomer 5 has a higher reactivity than the isomer 6 inphotopolymerisation. Such higher reactivity is demonstrated by the factthat the increase of the solid mixture of the invention is higher of atleast 2% than the increase of the content of dimer isomers in the samemixture.

This is a surprising result, because at our knowledge a regiospecificactivity had never been found before in photoinitiators.

In the following examples the measurement of the content of the dimerisomers and of the ratio between the two dimer isomers 5 and 6 in thehigh viscosity mixtures and in the solid mixtures reported in exampleswas carried out by HPLC (high performance liquid chromatography). Thechromatographic 20 conditions were: column C18, 4 μm, 150×3.9 mm;eluent: solvent A=methanol, solvent B=water; gradient from 70% A to 100%A in 10 min. 100% A 10 min; flow rate 0.8 ml/min, detector UV 254 nm.

EXAMPLE 1

The precipitation of the solid mixture is carried out with toluene assolvent (ε° 0.29) using a high viscosity mixture with a dimer content of85.1% and a ratio between the dimer isomers 5 and 6 of 1.93. This highviscosity mixture (Mixture 1) was obtained as reported in Example 10 ofthe patent U.S. Pat. No. 4,987,159.

14 kg of toluene are transferred into a heated reactor, set at atemperature of 120° C., and 28 kg of Mixture 1 are added under stirring.After complete dissolution the temperature is set at 20° C. and a smallportion of a previously precipitated product is added.

The precipitation mixture is left at 20° C. under stirring for 48 hours.The precipitate is filtered on a buckner and washed twice with toluene.

The amount of dried precipitate is 11.8 kg (Solid Mixture 1, yield41.3%); the content of the dimer isomers is 96.8% and the ratio of thedimer isomers 5 and 6 is 2.93

EXAMPLE 2

The precipitation of the solid mixture is carried out using ethylacetate (ε° 0.58) as solvent and according to Example 1, using 1000 g ofMixture 1 and 500 g of ethyl acetate, at a dissolution temperature of75° C., and at a precipitation temperature of 22–24° C. for 48 hours.

The amount of dried precipitate is 451 g (Solid Mixture 2, yield 45.1%);the content of the dimer isomers is 93.2% and the ratio between thedimer isomers 5 and 6 is 2.5.

EXAMPLE 3

Evaluation of the Photopolymerisation Reactivity of Solid Mixture 1

A formulation based on 75% (w/w) of Ebecryl 220 (urethane acrylateoligomer from UCB), 12.5% (w/w) of propoxylated glycerol triacrylate and12.5% (w/w) of hexanediol diacrylate was prepared and 4% (w/w) of SolidMixture 1 was added under stirring at room temperature.

A layer of 50 μm of the photoinitiated formulation was spread on acardboard and cross-linked using a Giardina® apparatus equipped with amedium pressure mercury lamp of 80 W/cm. The maximum speed ofcross-linking was 17.0 m/min. The photopolymerisation is consideredcomplete when the formulation resists surface abrasion (it is notdamaged after repeated z brushing using a sheet of paper pressed by athumb).

EXAMPLE 4

Evaluation of the Photopolymerisation Reactivity of Mixture 1

A formulation based on 75% (w/w) of Ebecryl 220 (urethane acrylateoligomer from UCB), 12.5% (w/w) of propoxylated glicerol triacrylate and12.5% (w/w) of hexanediol diacrylate was prepared and 4% (w/w) ofMixture 1 was added under stirring at room temperature.

A layer of 50 μm of the photoinitiated formulation was spread oncardboard and cross-linked using a Giardina( apparatus equipped with amedium pressure mercury lamp of 80 W/cm. The maximum speed ofcross-linking, measured according to Example 3, was 14.5 m/mint sComparing the results of Examples 3 and 4, an increase of content of thedimer isomers of 13.7% results in an increase of reactivity of 17.2%.

Comparing the results of Examples 3 and 4, an increase of content of thedimer isomers of 13.7% results in an increase of reactivity of 17.2%.

This difference shows a surprisingly higher reactivity of isomer 5compared to isomer 6.

1. A composition comprising solid mixtures of alpha-hydroxycarbonylderivatives of oligomers of alpha methylstyrene wherein the solidmixtures of alpha-hydroxycarbonyl derivatives of oligomers of alphamethylstyrene contain at least 90% of dimer isomers 5 and 6, and theratio of the dimer isomer 5 and the dimer isomer 6 is from about 2.5 toabout 7; wherein dimer isomer 5 has the structure:

and wherein dimer isomer 6 has the structure:


2. The composition of claim 1 wherein the solid mixtures ofalpha-hydroxycarbonyl derivatives of oligomers of alpha methylstyreneare prepared by precipitation from a mixture containing them.
 3. Thecomposition of claim 2 wherein the mixture from which the solid mixturesof alpha-hydroxycarbonyl derivatives of oligomers of alpha methylstyreneare precipitated contains at least 60% of the dimer isomers 5 and
 6. 4.A process for preparing solid mixtures of alpha-hydroxycarbonylderivatives of oligomers of alpha-methylstyrene wherein the solidmixture contains at least 90% of dimer isomers 5 and 6 and the ratio ofthe dimer isomer 5 and the dimer isomer 6 is from about 2.5 to about 7,comprising dissolving a high viscosity mixture of alpha-hydroxycarbonylderivatives of oligomers of alpha-methylstyrene in a solvent with apolarity of from about 0.1 to about 0.7 and with a ratio of solvent tomixture of from about 0.2 to about 4; keeping the solution at atemperature below about 40° C. for from about 10 to about 60 hours; andcollecting the thus obtained solid mixture.
 5. A process forphotopolymerisation of formulations containing at least one unsaturatedcompound comprising admixing a composition of claim 1 and an formulationincluding at least one unsaturated compound under conditions sufficientto photopolymerise the formulation.